Multiple media uploads excludes .mobi files

Hello,

Thank you for a very good plugin. We are using the metabox feature to upload multiple files to a custom post – these are ebooks, and the formats are pdf, epub and mobi. I have added them to the allowed mimetypes in WP, but when clicking to upload files, then selecting three files (the three versions of the same book), only two are included. It is always the .mobi file that is left out. Subsequently clicking Select file on the third (where the input field is empty), I can select the .mobi file and add it. It’s only when adding three files that this fails.

https://ww.wp.xz.cn/plugins/admin-page-framework/